Faculty Profiles - MAEKAWA, Nobuhiro

Recent discovery of neutrino large mixings implies the large mixings in the diagonalizing matrices
of ¯5 fields in SU(5) grand unified theory (GUT), while the diagonalizing matrices of 10 fields of
SU(5) are expected to have small mixings like Cabibbo-Kobayashi-Maskawa matrix. We calculate
the predictions of flavor changing nucleon decays (FCND) in SU(5), SO(10), and E6 GUT models
which have the above features for mixings. We found that FCND can be the main decay mode and
play an important role to test GUT models.

DOI： 10.1016/j.physletb.2017.02.028

Web of Science

Chiral Four-Dimensional Heterotic String Vacua from Covariant Lattices Foreword

Maekawa Nobuhiro

CHIRAL FOUR-DIMENSIONAL HETEROTIC STRING VACUA FROM COVARIANT LATTICES page： V - VI 2017

Neutrino masses and mixings as an evidence of GUT, and the impact to (flavor changing) nucleon decay

Maekawa, N; Muramatsu, Y

WORKSHOP ON NEUTRINO PHYSICS AND UNIFICATION, NEAR DETECTOR PHYSICS AND DARK MATTER (CETUP* 2016) Vol. 1900 2017

Leptogenesis in E6*U(1) SUSY GUT model Reviewed

Takuya Ishihara, Nobuhiro Maekawa, Mao Takegawa, Masato Yamanaka

Journal of High Energy Physics Vol. 1602 page： 108 2016.2

Language：English Publishing type：Research paper (scientific journal)

We study the thermal leptogenesis in the E 6 ×U(1) A SUSY GUT model in which realistic masses and mixings of quarks and leptons can be realized. We show that the sufficient baryon number can be produced by the leptogenesis in the model, in which the mass parameter of the lightest right-handed neutrino is predicted to be smaller than 10 8 GeV. The essential point is that the mass of the lightest right-handed neutrino can be enhanced in the model because it has a lot of mass terms whose mass parameters are predicted to be the same order of magnitude which is smaller than 10 8 GeV. We show that O(10) enhancement for the lightest right-handed neutrino mass is sufficient for the observed baryon asymmetry. Note that such mass enhancements do not change the predictions of neutrino masses and mixings at the low energy scale in the E 6 model which has six right-handed neutrinos. In the calculation, we include the effects of supersymmetry and flavor in final states of the right-handed neutrino decay. We show that the effect of supersymmetry is quite important even in the strong washout regime when the effect of flavor is included. This is because the washout effects on the asymmetries both of the muon and the electron become weaker than that of the tau asymmetry.

DOI： 10.1007/JHEP02(2016)108

arXiv

preheating with higher dimensional interaction Reviewed

Seishi Enomoto, Nobuhiro Maekawa, Tomohiro Matsuda

Physical Review D Vol. 91 ( 10 ) page： 103504 2015.5

Language：English Publishing type：Research paper (scientific journal)

Particle production caused by the oscillation after inflation is important since it explains reheating after inflation. On the particle theory side, we know that effective action may have additional higher dimensional terms (usually called nonrenormalizable terms) suppressed by the cutoff scale. Moreover, interaction between the inflaton and so-called moduli field will be higher dimensional. Therefore, if such higher dimensional interaction is significant for resonant particle production, one cannot avoid the effect in a preheating study. We explicitly calculated the required number of oscillations for the energy transfer. Consequently, cosmological history of an oscillating field and the moduli problem can be reconsidered.

DOI： 10.1103/PhysRevD.91.103504

The heavy gravitino, naturalness, and sizable anomaly mediation Reviewed

Nobuhiro Maekawa, Kenichi Takayama

Progress of Theoretical and Experimental Physics Vol. 093 page： 04 2014

Language：English Publishing type：Research paper (scientific journal)

We consider the situation in which m_{3/2}\sim O(100{\rm TeV}) for solving the gravitino problem and the other supersymmetry(SUSY) breaking parameters are O(1{\rm TeV}) for the naturalness. We point out that the anomaly mediation cancels out the renormalization group contribution to the gaugino masses and the sfermion masses other than the stop masses at a scale which is called the mirage scale. The situation is similar to the mirage mediation, in which special boundary conditions for the SUSY breaking parameters are required, though for the stop masses and the up-type Higgs mass, such cancellation at the mirage scale does not happen. Despite no cancellation for the up-type Higgs mass, we show that the little hierarchy problem becomes less severe in this situation. One advantage of this situation over the mirage mediation is that the stop mixing parameter A_t can be larger and therefore, smaller stop mass is sufficient for 125 GeV Higgs. When the mirage scale is around TeV scale, the SUSY breaking parameters induced by the gravity mediation at the grand unification scale can be observed directly by the TeV scale experiments.

DOI： DOI:10.1093/ptep/ptu118

Sizable D-term contributions as a signature of the E6*SU(2)F*U(1)A SUSY GUT model Reviewed

Nobuhiro Maekawa, Yu Muramatsu, Yoshihiro Shigekami

Progress of Theoretical and Experimental Physics Vol. 113 page： 02(18pages) 2014

Language：English Publishing type：Research paper (scientific journal)

We show that the sizable D-term contributions to sfermion mass spectrum can be signatures of certain GUT, E6×SU(2)F×U(1)A GUT. Note that these D-term contributions deviate the degenerate sfermion masses among different generations in this model. This is different from the previous works which have argued the D-term contributions, which deviate masses only between sfermions with different quantum charges, as a signature of GUT with larger rank unification group. Such D-terms are strongly constrained by the FCNC processes if the SUSY breaking scale is the weak scale. However, in E6×SU(2)F×U(1)A, natural SUSY type sfermion mass spectrum is obtained, and if the masses of 103 sfermions are larger than O(1TeV) to realize 126 GeV Higgs and the other sfermion masses are O(10TeV), then sizable D-term contribution is allowed. If the deviations by these D-terms can be observed in future experiments like 100 TeV proton collider or muon collider, we may confirm the E6×SU(2)F×U(1)A GUT.

DOI： 10.1093/ptep/ptu151

Nucleon decay via dimension 6 operators in anomalous U(1) SUSY GUT Reviewed

Nobuhiro Maekawa, Yu Muramatsu

Physical Review D 88 Vol. 88 page： 095008 2013

Language：English Publishing type：Research paper (scientific journal)

Nucleon lifetimes for various decay modes via dimension 6 operators are calculated in the anomalous U(1)_A GUT scenario, in which the unification scale \Lambda_u becomes smaller than the usual suersymmetric (SUSY) unification scale \Lambda_G=2\times 10^{16} GeV in general. Since the predicted lifetime \tau(p \rightarrow \pi^0 + e^c) becomes around the experimental lower bound though it is strongly dependent on the explicit models, the discovery of the nucleon decay in near future can be expected. We explain why the two ratios R_1 \equiv \Gamma_{n \rightarrow \pi^0 + \nu^c}/\Gamma_{p \rightarrow \pi^0 + e^c} and R_2 \equiv \Gamma_{p \rightarrow K^0 + \mu^c}/\Gamma_{p \rightarrow \pi^0 + e^c} are important in identifying grand unification group and we show that three anomalous U(1)_A SUSY GUT models with SU(5), SO(10) and E_6 grand unification group can be identified by measuring the two ratios. If R_1 is larger than 0.4, the grand unification group is not SU(5), and moreover if R_2 is larger than 0.3, the grand unification group is implied to be E_6.

DOI： 10.1103/PhysRevD.88.095008

Neutrino properties in E6xSU(2) SUSY GUT with spontaneous CP violation Reviewed

Nobuhiro Maekawa, Kenichi Takayama

Physical Review D Vol. 85 page： 095015 2012

Averaged Number of the Lightest Supersymmetric Particles in Decay of Superheavy Particle with Long Lifetime Reviewed

Yasuhiro Kurata, Nobuhiro Maekawa

Progress of Theoretical Physics Vol. 127 page： 657 2012

Heterotic E6 GUTs and Partition Functions Reviewed

Motoharu Ito, Shogo Kuwakino, Nobuhiro Maekawa, Sanefumi Moriyama, Keijiro Takahashi, Kazuaki Takei, Shunsuke Teraguchi, Toshifumi Yamashita

Journal of High Energy Physics Vol. 1112 page： 100 2011.12

Baryogenesis by B-L generation due to superheavy particle decay Reviewed

Seishi Enomoto, Nobuhiro Maekawa

Physical Review D Vol. 84 page： 096007 2011

E6 grand unified theory with three generations from heterotic string Reviewed

Motoharu Ito, Shogo Kuwakino, Nobuhiro Maekawa, Sanefumi Moriyama, Keijiro Takahashi, Kazuaki Takei, Shunsuke Teraguchi, Toshifumi Yamashita

Physical Review D Vol. 83 page： 091703 2011

Flavor structure of E6 GUT models Reviewed

Hidetoshi Kawase, Nobuhiro Maekawa

Progress of Theoretical Physics Vol. 123 page： 941-955 2010.6

Language：English Publishing type：Research paper (scientific journal)

It has been pointed out that in E6 grand unified theory with SU(2) family symmetry, the spontaneous CP violation can solve the supersymmetric CP problem. The scenario predicts V_{ub} \sim O(\lambda^4) rather than O(\lambda^3) which is naively expected value, because of a cancellation at the leading order. Since the experimental value of V_{ub} is O(\lambda^4), it must be important to consider the reason and the conditions for the cancellation. In this paper, we give a simple reason for the cancellation and show that in some E6 models such a cancellation requires that the vacuum expectation value (VEV) of the adjoint Higgs does not break U(1)_{B-L}. Note that this direction of the VEV plays an important role in solving the doublet-triplet splitting problem by Dimopoulos-Wilczek mechanism. In this E6 models, the experiments may measure the direction of the adjoint Higgs VEV by measuring the size of V_{ub} \sim O(\lambda^4).

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Papers - MAEKAWA, Nobuhiro